1. Field of the Invention
The present invention generally relates to methods and systems for inspecting a specimen using light scattered in different wavelength ranges. Certain embodiments relate to separately detecting scattered light having one or more wavelengths that are longer or shorter than an incident wavelength.
2. Description of the Related Art
Fabricating semiconductor devices such as logic and memory devices typically includes processing a specimen such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that typically involves transferring a pattern to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
During each semiconductor fabrication process, defects such as particulate contamination and pattern defects may be introduced into semiconductor devices. Such defects may be found either randomly on a specimen surface or may be repeated within each device formed on a specimen. For example, random defects may be caused by events such as contamination in a manufacturing environment and contamination in process chemicals used in fabrication of a semiconductor device. Defects may also be formed in a systematic fashion over time and due to individual process marginalities and interactions of multiple processes. Defects caused by individual process marginalities or by interactions between multiple processes may result in defects such as a film thickness variation or a lateral dimension variation due to dose variation. Such defects may, in turn, result in a defect in a semiconductor device formed on the specimen such as bridging between two conductive structures thereby forming a short between the structures. Defects repeated within each semiconductor device formed on an entire specimen may, for example, be systematically caused by contamination or defects found on a reticle, or a mask. Contamination or defects on a reticle may be transferred along with a device pattern to a resist during a lithography process.
As the dimensions of advanced semiconductor devices continue to shrink, the presence of defects in the semiconductor devices limits the successful fabrication, or yield, of a semiconductor device. For example, a reticle defect reproduced in a resist patterned during lithography may cause an open circuit or a short circuit in a semiconductor device formed in subsequent processing. Because fabrication of a semiconductor device includes many complex process steps, the adverse effects of defects on total yield may increase exponentially if an error that is caused by a defect is propagated throughout an entire manufacturing process or operation over time.